1. Field of the Invention
The present invention relates to a fuel cut control apparatus of an internal combustion engine.
2. Description of the Related Art
In an exhaust gas purifying catalyst (hereinafter, also simply called “catalyst”) such as a three-way catalyst which is placed in an exhaust passage of a vehicle, sulfur (S) is adsorbed by ceria (CeO2) in the catalyst when an air-fuel ratio is lean, and when it is rich, the sulfur is desorbed. It is known that the desorbed sulfur oxide (SO2) is reduced and hydrogen sulfide (H2S) is generated. The H2S has such an odor that gives a discomfort to a driver (hereinafter, called “exhaust odor”).
As a control technique concerning suppression of H2S, for example, Japanese Patent Application Laid-Open under No. 2003-65127 discloses the art of suppressing the generation of the above-described H2S by controlling the air-fuel ratio to be lean (namely, to establish oxidation atmosphere with excessive oxygen) when the vehicle is idling and the temperature of the catalyst is lower than a predetermined temperature. Other than this, Japanese Patent Application Laid-Open under No. 2000-204937 discloses the control technique concerning suppression of H2S, and Japanese Patent Application Laid-Open under No. 2002-327641 discloses the technique concerning the control of oxygen storage amount of a catalyst.
In a fuel injection amount control for an internal combustion engine, fuel cut which temporarily stops fuel injection is conventionally performed. For example, when the throttle valve is completely closed and the number of engine revolution is equal to or higher than a predetermined number (namely, when the internal combustion engine is in a decelerating operation state), it is determined that the driving state is in the decelerating operation state requiring no fuel supply, and fuel injection is stopped, thus performing fuel cut to enhance fuel consumption efficiency, purify exhaust gas and prevent heating of the exhaust gas purifying catalyst.
The execution of such fuel cut sometimes causes deterioration of the exhaust gas purifying catalyst provided in the exhaust system. Namely, the fuel cut induces oxidation atmosphere in the exhaust system, and it is found out that, if the fuel cut is executed in the state in which the temperature of the catalyst is high, the peripheral area of the exhaust purifying catalyst becomes the oxidation atmosphere at high temperature, which causes the catalyst to deteriorate early. Thus, for example, Japanese Patent Application Laid-Open under No. 8-144814 discloses the art concerning the fuel cut control which stops execution of the fuel cut when the temperature of the exhaust gas purifying catalyst is high even if the internal combustion engine is in the decelerating operation state.
However, in the fuel cut execution stopping control as described above, there is the problem that sufficient oxygen cannot be supplied to the catalyst if the execution of the fuel cut is stopped when the oxygen storage amount of the exhaust gas purifying catalyst is small, and therefore the inside of the catalyst becomes the reducing atmosphere thereafter, which sometimes causes exhaust odor due to H2S.